1. Field of the Invention
The instant invention relates to a method of increasing the permeability of epithelial cell chloride (Cl.sup.-) channels and a method of treating cystic fibrosis. In particular, the method comprises administering a nontoxic, nonionic surfactant having (1) a critical micelle concentration of less than about 10 mM and a hydrophile-lipophile balance number of from about 10 to 20, and (2) a hydrophobic organic group and a hydrophilic polyol. Additionally provided are compositions for treating cystic fibrosis and for increasing permeability of epithelial cells to chloride.
2. Background Art
Cystic fibrosis is the most common autosomal recessive disease in Caucasians. The disease is a complex disorder mainly affecting organs with epithelial cell linings, including the airways, pancreas, intestine, sweat glands and male genital tract. The primary defect in CF is a relative impermeability of the epithelial cells of these organs to chloride ion. The lung and the GI tract are the predominant organ systems affected in this disease and the pathology is characterized by blocking of the respiratory and GI tract with viscous mucus. The Cl.sup.- impermeability in affected tissues is due to mutations in a specific chloride channel, the cystic fibrosis transmembrane conductance regulator protein (CFTR), which prevents normal passage of Cl.sup.- ions through the cell membrane (Welsh et al., Neuron, 8:821-829 (1992)). There is no effective treatment for the disease, and therapeutic research is focused on gene therapy and/or activating the defective or other Cl.sup.- channels in the cell membrane to normalize Cl.sup.- permeability (Tizzano et al., J. Pediat., 120:337-349 (1992)). Damage to the lung due to mucus blockage, frequent bacterial infections and inflammation is the primary cause of morbidity and mortality in CF patients and although maintenance therapy has improved the quality of patients' lives, the median age at death is around 30 years.
A major advance in our understanding of the metabolic basis for cystic fibrosis and in the development of therapies to treat the disease came with the discovery and characterization of the cystic fibrosis transmembrane conductance regulator (CFTR), the specific chloride channel which is defective in CF (see Welsh et al., for review). All cases of CF are due to mutations in the CFTR protein, the most common being a deletion of the phenylalanine residue at position 508 of the protein (.DELTA.F508). A model cell to study the structure and function of native CFTR is the T84 cell line derived from a colonic adenocarcinoma which expresses high levels of the CFTR chloride channel protein (Cohn et al., Proc. Natl. Acad. Sci. USA, 89:2340-2344 (1992)).
A breakthrough in the development of a continuous cell line expressing the major mutation in CFTR found in CF was the establishment of a pancreatic adenocarcinoma cell line from a patient with cystic fibrosis (Schoumacher et al., Proc. Natl. Acad. Sci. USA, 87:4012-4016 (1990)). This cell line, designated CFPAC-1, is homozygous for the .DELTA.F508 mutation and expresses the characteristic Cl.sup.- channel defect in CF, the inability of the channel to be activated by forskolin, cAMP or phosphodiesterase inhibitors, all agents which activate CFTR in T84 cells. The Cl.sup.- channel defect in this cell line could be corrected by introducing functional CFTR cDNA into the cell by transduction with a CFTR expressing retrovirus (Drumm et al., Cell, 62:1227-1233 (1990)).
The efflux of .sup.125 I- has been shown to be a simple assay for agonist-regulated Cl.sup.- channels in salt secreting epithelial cells (Venglarik et al., Am. J. Physiol., 259:C358-C364 (1990)). The activation of the defective and/or alternative functioning chloride channels in cystic fibrosis epithelial cells in order to normalize their permeability to chloride is one of the primary therapeutic goals of the treatment of cystic fibrosis and has not yet been accomplished (Boat, T. F., Welsh, M. J. and Beaudet, A. L., "Cystic Fibrosis" in The Metabolic Basis of Inherited Disease, pp. 2649-2680 (Striver, C. R., Beaudet, A. L., Sly, W. S. and Valle, D. eds.) McGraw-Hill, New York (1989)). Thus, there exists an urgent need for a treatment that increases the permeability of epithelial cells to chloride and thereby can be used to treat cystic fibrosis. Such a treatment would be most beneficial if it were nontoxic and nonirritating to the epithelial cell linings, yet allowed the restoration of the proper chloride equilibrium of the cells, as well as the clearing of existing mucus. The present invention satisfies this need by providing methods and compounds which can therapeutically relieve both the cause of the manifestations of cystic fibrosis, as well as the manifestations themselves.